JP5591523B2 - In-Ga-Zn-O-based oxide sintered sputtering target excellent in stability during long-term film formation - Google Patents

Description

  The present invention relates to a sputtering target for forming an oxide thin film such as an oxide semiconductor or a transparent conductive film, particularly for forming a thin film transistor.

  An amorphous oxide film made of indium oxide and zinc oxide, or made of indium oxide, zinc oxide and gallium oxide has visible light transmittance and wide electrical characteristics from conductors, semiconductors to insulators. Attention has been paid to transparent conductive films and semiconductor films (used for thin film transistors and the like).

  As a method for forming the oxide film, there are physical film formation such as sputtering, pulse laser deposition (PLD), and vapor deposition, and chemical film formation such as a sol-gel method. As a method for uniformly forming a film, physical film formation such as a sputtering method has been mainly studied.

  When an oxide thin film is formed by physical film formation such as sputtering, a target made of an oxide sintered body is used in order to form a film uniformly, stably and efficiently (at a high film formation rate). It is common.

As a typical oxide film (conductive film / semiconductor film), for example, an oxide film made of indium oxide, zinc oxide, or gallium oxide can be given. As a target (mainly a sputtering target) for producing these oxide films (usually amorphous films), a known crystal type composition such as InGaZnO ₄ , In ₂ Ga ₂ ZnO ₇ or a composition close to that is known. Is mainly considered.

For example, Patent Document 1 discloses a target including a homologous structure of InGaZnO ₄ (InGaO ₃ (ZnO)). Patent Document 2 discusses a production method that does not generate a highly insulating Ga ₂ O ₃ crystal phase. Patent Documents 3 and 4 disclose a sputtering target mainly composed of ZnO. However, when only a target for an optical recording medium or a transparent electrode is studied, a thin film transistor is formed using such a target. The effect on transistor characteristics has not been studied. Patent Document 5 discusses the development of a target utilizing the characteristics of a mixture such as a target composed of a mixture of a hexagonal layered compound of InGaZnO ₄ and a spinel structure of ZnGa ₂ O ₄ . However, in these examinations, examination of the properties of the target surface and internal crystal forms, etc., and matching these crystal forms are not considered.

  Patent Document 6 discloses an example in which an amorphous oxide semiconductor film and a thin film transistor are formed using an In—Ga—Zn—O sintered body having a metal composition ratio In: Ga: Zn = 30: 15: 55. Has been. However, the properties of the appropriate sputtering target and the manufacturing method have not been studied, and when such a sintered body is used as a target, the Ga content ratio of the thin film is about two-thirds of the Ga content ratio of the target. There was a problem of becoming extremely small. This suggests that there are large distributions of various properties including the composition in the target, but no study has been made on the uniformity of the target properties.

  Unlike the production of silicon thin film transistors using plasma vapor deposition (PECVD) with conventional gas supply, the production of thin film transistors using sputtering targets has become more practical. The film was formed over a long period of time, such as thin film transistor performance changes due to changes in the properties of the thin film obtained and fluctuations in the film formation speed, and fine adjustment of the film formation conditions was required. The problem of instability has become apparent. In addition, it has become clear that this effect is particularly significant in a semiconductor element typified by a thin film transistor (TFT) as compared with the case where a transparent conductive film is formed. As described above, various studies have been made on a target for producing an oxide thin film. However, when a single target is used for a long period of time to form a film, the properties of the obtained thin film and, consequently, the performance of the thin film transistor are evaluated. Stability is not considered.

JP 2007-73312 A JP 2007-223849 A WO2004 / 079038 Japanese Patent No. 3644647 WO2008 / 072486 JP 2008-53356 A

  An object of the present invention is to provide a sputtering target having excellent stability of characteristics of a thin film obtained when film formation is performed over a long period of time.

  In order to achieve the above object, as a result of intensive studies by the present inventors, the instability of the characteristics of the thin film when the film is formed for a long period of time is caused by the property of the target (specific resistance, etc.) by continuing the sputtering for a long period of time. I found out that it was to change. Furthermore, when a sputtering target made of indium oxide, zinc oxide and gallium oxide is formed for a long period of time, a change in crystal form (change in crystal type) occurs on the surface subjected to sputtering, which is the instability described above. I found out that it is the cause of.

  Conventionally, this problem has not been manifested in sputtering targets made of indium oxide and tin oxide, and sputtering targets made of indium oxide and zinc oxide. This is because the inclusion of both gallium and zinc results in a diversity of crystal forms that can be produced, including layered compounds, and due to differences in the formation temperature, the composition ratio varies due to slight differences in conditions and evaporation of components. This is presumably due to the change in crystal form.

  Furthermore, select a manufacturing method and manufacturing conditions suitable for obtaining a suitable composition ratio. For example, the molded body having a large thickness is heated at a slow speed to produce a sintered body, and the surface is sufficiently ground. It has been found that this can be solved by using a target and adopting conditions for generating an appropriate crystal form for each composition.

Then, by using the sputtering target having the same surface portion and the same internal crystal form (in the case of two or more crystal types, the combination of crystal types is the same), the film is formed for a long time. The film formation rate did not change much even if the process was performed, and the change in characteristics of TFTs produced using the thin film obtained was successfully suppressed, and the present invention was completed.
It has also been found that the use of the present invention reduces the difference between the composition of the target and the thin film, and improves the problem that the Ga content ratio of the thin film becomes extremely smaller than the Ga content ratio of the target.

According to this invention, the manufacturing method of the following sputtering targets and sputtering targets is provided.
1. Including In, Zn, and Ga,
A sputtering target comprising an oxide sintered body in which the crystal types of the surface and internal compounds are substantially the same.
2. 2. The ratio 1 / R2 of the specific resistance (R1) of the surface of the oxide sintered body and the specific resistance (R2) at a depth of t / 2 mm from the surface is 0.4 or more and 2.5 or less. Sputtering target.
3. 3. The sputtering target according to 1 or 2 above, wherein the composition ratio (atomic ratio) of In, Zn, and Ga in the oxide sintered body satisfies any of the following regions 1 to 6.
Region 1
Ga / (In + Ga + Zn) ≦ 0.50
0.58 ≦ In / (In + Zn) ≦ 0.85
In / (In + Ga) ≦ 0.58
Region 2
Ga / (In + Ga + Zn) ≦ 0.50
0.20 ≦ In / (In + Zn) <0.58
In / (In + Ga) ≦ 0.58
Region 3
0.20 <Ga / (In + Ga + Zn)
0.51 ≦ In / (In + Zn) ≦ 0.85
0.58 <In / (In + Ga)
Region 4
0.00 <Ga / (In + Ga + Zn) <0.15
0.20 ≦ In / (In + Zn) <0.51
0.58 <In / (In + Ga)
Region 5
0.00 <Ga / (In + Ga + Zn) ≦ 0.20
0.51 ≦ In / (In + Zn) ≦ 0.85
Region 6
0.15 ≦ Ga / (In + Ga + Zn)
In / (In + Zn) <0.51
0.58 <In / (In + Ga)
4). 4. The sputtering target according to 3 above, wherein the substantially same crystal type consists of only one type of crystal type.
5. 5. The sputtering target according to 4 above, wherein the one type of crystal type is a homologous crystal structure represented by In ₂ Ga ₂ ZnO ₇ and satisfies the composition ratio of the region 1.
6). 5. The sputtering target according to 4 above, wherein the one type of crystal type is a homologous crystal structure represented by InGaO ₃ (ZnO) and satisfies the composition ratio of the region 2 or the region 3.
7). The one type of crystal type is 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and The sputtering target according to 4 above, which has a crystal structure having an X-ray diffraction peak of Cukα rays at 56.5 ° to 59.5 ° and satisfies the composition ratio of the region 4.
8). The substantially identical crystal type includes a spinel crystal structure represented by ZnGa ₂ O ₄ and a bixbite crystal structure represented by In ₂ O ₃ , and satisfies the composition ratio of the region 1 or region 3. 4. The sputtering target according to 3 above.
9. The substantially identical crystal types are 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and The crystal structure having an X-ray diffraction peak of Cukα rays at 56.5 ° to 59.5 ° and a bixbite crystal structure represented by In ₂ O ₃ and satisfying the composition ratio of the region 5 3. The sputtering target according to 3.
10. The substantially identical crystal types are 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and The crystal structure having an X-ray diffraction peak of Cukα rays at 56.5 ° to 59.5 ° and a homologous crystal structure represented by InGaO ₃ (ZnO), and satisfying the composition ratio of the region 6 3. The sputtering target according to 3.
11. The manufacturing method of the sputtering target of any one of said 4, 5, 6, and 8 including the process of following (a)-(e).
(A) A step of preparing a mixture by mixing raw material compound powders,
(B) forming the mixture to prepare a molded body having a thickness of 6.0 mm or more;
(C) a step of heating the atmosphere at a heating rate of 3 ° C./min or less,
(D) a step of further sintering the heated body at 1280 ° C. to 1520 ° C. for 2 hours to 96 hours to obtain a sintered body having a thickness of 5.5 mm or more,
(E) Grinding the surface of the sintered body by 0.25 mm or more. The manufacturing method of the sputtering target of said 5 containing the process of following (a)-(e).
(A) A step of preparing a mixture by mixing raw material compound powders,
(B) forming the mixture to prepare a molded body having a thickness of 6.0 mm or more;
(C) a step of heating the atmosphere at a heating rate of 3 ° C./min or less,
(D) a step of further sintering the temperature-increased molded body at 1350 ° C. to 1540 ° C. for 2 hours to 36 hours to obtain a sintered body having a thickness of 5.5 mm or more;
(E) Grinding the surface of the sintered body by 0.25 mm or more. The manufacturing method of said 8 sputtering target including the process of following (f)-(i).
(F) mixing the raw material compound powder to prepare a mixture;
(G) forming the mixture to prepare a molded body;
(H) a step of heating the atmosphere at a heating rate of 10 ° C./min or less,
(I) A step of further sintering the temperature-increased compact at 1100 ° C. to 1350 ° C. for 4 hours to 96 hours.

According to the present invention, it is possible to provide a sputtering target that is excellent in stability of characteristics of a thin film obtained when film formation is performed over a long period of time.
According to the present invention, stable thin film transistor characteristics can be obtained even when film formation is performed over a long period of time.

It is a schematic diagram showing a structure of a channel stopper type thin film transistor (inverse stagger type thin film transistor) according to the present invention.

  The sputtering target of the present invention (hereinafter referred to as the target of the present invention) is composed of an oxide sintered body containing In, Zn, and Ga and having substantially the same crystal type of the surface and the inner compound. It is characterized by.

If the surface type of the target and the crystal type of the internal compound are substantially the same, even if the film is formed over a long period of time using a single target, there will be no fluctuation in the properties of the thin film obtained. .
Here, “substantially” means that the types of crystal types identified when the surface and the surface cut into the inside are measured by X-ray diffraction measurement (XRD) may be the same.

  For example, when the average thickness is tmm, the crystal form of the target surface and the internal compound are cut at t / 2 mm from the surface, and the crystal form of the surface compound and t / The crystal form of the compound at a depth of 2 mm is determined by analysis by X-ray diffraction measurement (XRD).

  The crystal structure of the surface of the sputtering target can be confirmed from the X-ray diffraction pattern obtained by directly measuring the target surface by X-ray diffraction.

  The crystal structure of the deep part of the sputtering target can be confirmed from the obtained X-ray diffraction pattern by cutting the target horizontally on the surface, measuring the obtained cut surface directly by X-ray diffraction.

The target cutting method is, for example, as follows.
Apparatus: Maruto Co., Ltd. Million-Cutter 2 MC-503N
Condition: Diamond blade φ200mm
procedure:
1. Heat the absorption plate (alumina plate) and apply Adfix (adhesive manufactured by Marto) on the top surface.
2. After placing the target, fix the target by quenching with water.
3. Set the absorption plate on the device and cut the target.
4). Thereafter, steps 1 to 3 are repeated so as to obtain an arbitrary cutting surface.

The measurement conditions of X-ray diffraction are as follows, for example.
Device: Rigaku Ultima-III
X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
2θ-θ reflection method, continuous scan (1.0 ° / min)
Sampling interval: 0.02 °
Slit DS, SS: 2/3 °, RS: 0.6 mm

  The crystal type can be specified by checking with a JCPDS card for those registered in a JCPDS (Joint Committee of Powder Diffraction Standards) card.

  If the structure is judged by the crystal structure X-ray diffraction pattern, oxygen may be excessive or insufficient (oxygen deficiency) (may be shifted according to the stoichiometric ratio) or oxygen deficiency. It is preferable to have If the oxygen is excessive, the resistance may be too high when the target is used.

In addition to having the same crystal type, the target of the present invention preferably has substantially the same peak intensity ratio when it contains two or more crystal types. The comparison of the peak intensity ratio is performed by the ratio of the maximum peak heights of the respective crystal types. The ratio of the maximum peak heights is compared, and if the difference is ± 30% or less, it is judged that they are almost the same. The difference is more preferably ± 15% or less, particularly preferably ± 5% or less.
It can be expected that the smaller the difference in the ratio of the maximum peak heights, the less the variation in the properties of the thin film obtained when used over a long period of time.

  The target of the present invention may contain a metal element other than the above-described In, Ga, and Zn, for example, Sn, Ge, Si, Ti, Zr, and Hf, as long as the effects of the present invention are not impaired.

  In the present invention, the metal element contained in the target does not contain elements other than impurities that are inevitably contained depending on the raw material, the manufacturing process, etc., and may be only In, Ga, and Zn.

  Both the crystal grain diameter on the surface and the crystal grain diameter at a depth of t / 2 mm from the surface are preferably 20 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less.

  If the crystal grain sizes of the surface and the deep part are greatly different, there is a possibility that the discharge conditions are different.

  In the target of the present invention, the ratio R1 / R2 of the specific resistance (R1) on the surface of the oxide sintered body and the specific resistance (R2) at a depth of t / 2 mm from the surface is 0.4 to 2.5. Preferably there is.

  R1 / R2 is preferably 0.4 or more and 2.5 or less, more preferably 0.5 or more and 2 or less, and particularly preferably 0.67 or more and 1.5 or less.

  When R1 / R2 is less than 0.4 or more than 2.5, the properties (specific resistance, etc.) of the target change depending on when the target is used and when it is consumed over a long period of time. There is a risk of instability such as a change in speed or a change in the characteristics of the manufactured TFT.

  In the target of the present invention, it is preferable that the composition ratio (atomic ratio) of In, Zn, and Ga of the oxide sintered body satisfies any of the following regions 1 to 6.

Region 1
Ga / (In + Ga + Zn) ≦ 0.50
0.58 ≦ In / (In + Zn) ≦ 0.85
In / (In + Ga) ≦ 0.58
Region 2
Ga / (In + Ga + Zn) ≦ 0.50
0.20 ≦ In / (In + Zn) <0.58
In / (In + Ga) ≦ 0.58
Region 3
0.20 <Ga / (In + Ga + Zn)
0.51 ≦ In / (In + Zn) ≦ 0.85
0.58 <In / (In + Ga)
Region 4
0.00 <Ga / (In + Ga + Zn) <0.15
0.20 ≦ In / (In + Zn) <0.51
0.58 <In / (In + Ga)
Region 5
0.00 <Ga / (In + Ga + Zn) ≦ 0.20
0.51 ≦ In / (In + Zn) ≦ 0.85
Region 6
0.15 ≦ Ga / (In + Ga + Zn)
In / (In + Zn) <0.51
0.58 <In / (In + Ga)

A more preferable range of each region is as follows.
Region 1
Ga / (In + Ga + Zn) ≦ 0.45
0.58 ≦ In / (In + Zn) ≦ 0.80
In / (In + Ga) ≦ 0.56
Region 2
Ga / (In + Ga + Zn) ≦ 0.40
0.35 ≦ In / (In + Zn) <0.58
In / (In + Ga) ≦ 0.58
Region 3
0.20 <Ga / (In + Ga + Zn)
0.60 ≦ In / (In + Zn) ≦ 0.85
0.60 <In / (In + Ga)
Region 4
0.09 <Ga / (In + Ga + Zn) <0.15
0.35 ≦ In / (In + Zn) <0.48
Region 5
0.09 <Ga / (In + Ga + Zn) ≦ 0.20
0.53 ≦ In / (In + Zn) ≦ 0.75
Region 6
0.17 ≦ Ga / (In + Ga + Zn)
0.35 ≦ In / (In + Zn) <0.48
0.60 <In / (In + Ga)
A more preferable range of the region 6 is as follows.
Region 6
0.18 <Ga / (In + Ga + Zn)
0.38 <Zn / (In + Ga + Zn) ≦ 0.50

The characteristics of each region are as follows.
Region 1: Fabrication of TFT with low photocurrent is possible
Possible to produce TFT with high resistance to mixed acid
A target substantially consisting of a single crystal type (In ₂ Ga ₂ ZnO ₇ ) can be produced. In region 1, the production conditions such as the sintering temperature are adjusted, or a trace amount of dopant such as Sn is contained. , In ₂ Ga ₂ ZnO ₇ crystal form can be generated. In addition, an oxide sintered body in which a crystal type other than the crystal type of In ₂ Ga ₂ ZnO ₇ is not confirmed by XRD can be generated. By having a crystal type of In ₂ Ga ₂ ZnO ₇ , conductivity can be increased by a layered structure.
In the region 1, the crystal types of In ₂ O ₃ and ZnGa ₂ O ₄ can be included by adjusting the production conditions such as the sintering temperature. By having the crystal types of In ₂ O ₃ and ZnGa ₂ O ₄ , it is easy to generate oxygen vacancies in In ₂ O ₃ without performing heat treatment in a reducing atmosphere, and the specific resistance can be reduced. In addition, when this crystal type is included, the grinding amount is small, or it is easy to match the crystal types of the surface and the center without grinding. This seems to be because this crystal form is stable at a relatively low temperature.

Region 2: TFT with low photocurrent can be fabricated
Possible to produce a target consisting essentially of a single crystal type (InGaZnO ₄ )

Region 3: TFT with slightly high mobility and slightly low S value
In the region 3 where the photocurrent is small when the TFT is manufactured, the In ₂ O ₃ crystal type can be included by adjusting the manufacturing conditions such as the sintering temperature. By having a crystal form of In ₂ O _3, without performing heat treatment in a reducing atmosphere becomes easy to generate the oxygen defects in the In ₂ O _3, it is possible to lower the resistivity.
In region 3, the crystal form of the homologous structure represented by In ₂ Ga ₂ ZnO ₇ or InGaZnO ₄ by adjusting the production conditions such as the sintering temperature, although the ratio of In to Ga is not 1: 1. Can be generated. By having a crystal form of a homologous structure, conductivity can be increased by a layered structure.

Region 4: TFT with high mobility and low S value
Enables the production of targets consisting essentially of a single crystal type
It is easy to reduce the specific resistance of the target. In the region 4, it is possible to produce a target substantially consisting of a single crystal type by adjusting the production conditions such as the sintering temperature. By being substantially single, the uniformity of the target is improved. In addition, conductivity is improved.

Region 5: TFT with very high mobility and low S value
It is easy to reduce the specific resistance of the target. In region 5, 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to A target including a crystal structure having X-ray diffraction peaks of Cukα rays at 56.5 ° and 56.5 ° to 59.5 ° and a crystal type represented by In ₂ O ₃ can be manufactured. This combination of crystal types facilitates generation of oxygen vacancies in In ₂ O ₃ without performing heat treatment in a reducing atmosphere, and can reduce the specific resistance.
Further, the sputtering target having the composition of the region 5 is suitable for obtaining a thin film transistor with high mobility in which a semiconductor layer is thinned.

Region 6: TFTs with slightly high mobility and small S values can be fabricated
(Better photocurrent, mixed acid resistance, and moisture resistance than region 4)
In region 6, 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and 56.5 °. A target including a crystal structure having an X-ray diffraction peak of Cukα rays at ˜59.5 ° and a crystal type represented by InGaZnO ₄ can be produced. The conductivity is improved by the homologous structure.

When a TFT is fabricated using the target of the present invention, the photocurrent can be expected to decrease as Ga / (In + Zn + Ga) is larger than 0 and larger.
In addition, the smaller the Ga / (In + Zn + Ga) is 0.50 or less, the better the mobility and S value can be expected.

When a TFT is manufactured using the target of the present invention, the improvement in mobility can be expected as In / (In + Zn) is 0.20 or more and is larger.
Moreover, it can be expected that the smaller the In / (In + Zn) is 0.80 or less, the easier it is to adjust normally-off.

In regions 1 and 2 having a large amount of Ga, when film formation is performed by sputtering, changes in film formation rate and carrier density are relatively sensitive to oxygen partial pressure, so slight fluctuations and unevenness can be obtained. The uniformity of the thin film characteristics may be disturbed or the reproducibility may be reduced.
In terms of the sensitivity of the film formation rate and carrier density to changes in oxygen partial pressure, the regions 3 to 6 are preferable, and the regions 4 and 5 are particularly preferable.

  In the target of the present invention, the substantially same crystal type may consist of only one type of crystal type.

  In the case of consisting of only one type of crystal, it can be expected to improve the uniformity of the target physical properties and the appearance (suppression of occurrence of uneven color, white spots, black spots, etc.). In some cases, an improvement in the strength (bending strength or impact strength) of the target can be expected.

In the target of the present invention, it is preferable that the one type of crystal type has a homologous crystal structure represented by In ₂ Ga ₂ ZnO ₇ and satisfy the composition ratio of the region 1.

A crystal structure represented by In ₂ Ga ₂ ZnO ₇ (or (InGaO ₃ ) ₂ ZnO) showing a (YbFeO ₃ ) ₂ FeO type crystal structure is called a “hexagonal layered compound” or “a crystal structure of a homologous phase”. A crystal composed of a “natural superlattice” structure having a long period in which several crystal layers of different substances are stacked. When the crystal cycle or thickness of each thin film layer is on the order of nanometers, depending on the combination of the chemical composition of these layers and the thickness of the layers, it differs from the properties of a single substance or a mixed crystal in which each layer is uniformly mixed. Unique characteristics can be obtained. The crystal structure of the homologous phase is such that, for example, the X-ray diffraction pattern measured directly from the pulverized target, the cut piece or the target itself matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. It can be confirmed from. Specifically, it can be confirmed from the coincidence with the crystal structure X-ray diffraction pattern of the homologous phase obtained from a JCPDS (Joint Committee of Powder Diffraction Standards) card.
The crystal structure represented by In ₂ Ga ₂ ZnO ₇ is JCPDS card no. 38-1097.

This crystal type can be easily obtained by including Sn (tin) in the composition of region 1 in the following composition ratio (atomic ratio).
0.005 <Sn / (In + Ga + Zn + Sn) <0.10
The range of the Sn content is more preferably as follows.
0.01 <Sn / (In + Ga + Zn + Sn) <0.05

In order to obtain the present crystal type (a homologous crystal structure represented by In ₂ Ga ₂ ZnO ₇ ), the sintering temperature is preferably 1350 ° C. to 1540 ° C., more preferably 1380 to 1500 ° C.

In the target of the present invention, it is preferable that one type of crystal type has a homologous crystal structure represented by InGaO ₃ (ZnO) and satisfy the composition ratio of the region 2 or the region 3.

The crystal structure represented by InGaO ₃ (ZnO) _m (m is an integer of 1 to 20) is also a “hexagonal layered compound” or “a crystal structure of a homologous phase”.
The crystal structure represented by InGaO ₃ (ZnO) is JCPDS card no. 38-1104.

InGaO ₃ (ZnO) is a case where m = 1 of InGaO ₃ (ZnO) _m (m is an integer of 1 to 20), and may be described as InGaZnO ₄ .

  In the target of the present invention, one type of crystal type is 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 °. It is preferable that the crystal structure has X-ray diffraction peaks of Cukα rays at ˜56.5 ° and 56.5 ° to 59.5 °, and the composition ratio of the region 4 is satisfied.

  This crystal type oxide crystal is not a JCPDS (Joint Committee of Powder Diffraction Standards) card, and is a novel crystal that has not been confirmed so far.

The X-ray diffraction chart of this oxide crystal shows a crystal structure represented by InGaO ₃ (ZnO) ₂ (JCPDS: 40-0252) and a crystal represented by In ₂ O ₃ (ZnO) ₂ (JCPDS: 20-1442). Similar to structure. However, the oxide of the present invention has a peak peculiar to InGaO ₃ (ZnO) ₂ (the peak in the region A) and a peak peculiar to In ₂ O ₃ (ZnO) ₂ (the peaks in the regions D and E). In addition, InGaO ₃ (ZnO) ₂ and In ₂ O ₃ (ZnO) ₂ have peaks that are not observed (the region B). Therefore, the oxide of the present invention is different from InGaO ₃ (ZnO) ₂ and In ₂ O ₃ (ZnO) ₂ .

The feature of this new crystal type is that the following condition 1 is satisfied.
In the chart obtained by X-ray diffraction measurement (Cukα ray), diffraction peaks are observed in the following areas A to E.

Condition 1
A. Incident angle (2θ) = 7.0 ° to 8.4 ° (preferably 7.2 ° to 8.2 °)
B. 2θ = 30.6 ° to 32.0 ° (preferably 30.8 ° to 31.8 °)
C. 2θ = 33.8 ° to 35.8 ° (preferably 34.5 ° to 35.3 °)
D. 2θ = 53.5 ° to 56.5 ° (preferably 54.1 ° to 56.1 °)
E. 2θ = 56.5 ° to 59.5 ° (preferably 57.0 ° to 59.0 °)

Furthermore, it is preferable to satisfy the following condition 2.
Condition 2
One of the diffraction peaks observed at 2θ of 30.6 ° to 32.0 ° (region B) and 33.8 ° to 35.8 ° (region C) is a main peak, and the other is a sub peak. It is. Here, the main peak refers to the highest peak of the crystalline XRD pattern, and the sub peak refers to the second peak.

  In the target of the present invention, substantially the same crystal type may be composed of two or more types of crystal types.

In the target of the present invention, the substantially same crystal type includes a spinel crystal structure represented by ZnGa ₂ O ₃ and a bixbite crystal structure represented by In ₂ O ₃ , and the region 1 or region 3 described above. It is preferable that the composition ratio is satisfied.

By providing the spinel crystal structure represented by ZnGa ₂ O ₄ , generation of Ga ₂ O ₃ that is an insulator can be expected to be suppressed. When Ga ₂ O ₃ that is an insulator is generated, there is a risk that the frequency of abnormal discharge increases, the resistance of the target increases, and the like.
By including a bixbite crystal structure represented by In ₂ O ₃ , it is easy to manufacture a target having a low specific resistance without performing a reduction treatment.

  It is preferable that the oxygen content of the tissue having a large In content is lower than the oxygen content of other surrounding portions. The oxygen content of each tissue can be confirmed by a composition distribution using an electron probe microanalyzer (EPMA).

Further, the lattice constant a of the bixbyite structure represented by In ₂ O ₃ is preferably 10.14 or less, more preferably 10.10 or less, and particularly preferably 10.08 or less. The lattice constant a is obtained by XRD fitting. If the lattice constant is small, it can be expected that the specific resistance can be lowered by improving the mobility.

  This crystal type (including spinel crystal structure and bixbite crystal structure) can be expected to be obtained by sintering at 1100 ° C. to 1350 ° C. with the composition of region 1 or region 3.

  If this crystal form can be generated, the types of crystal forms on the surface and in the deep part, even when the average thickness of the oxide sintered body is less than 5.5 mm or the surface grinding of the sintered body is less than 0.3 mm May be able to produce sputtering targets that are substantially the same.

In the target of the present invention, substantially the same crystal type is 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 °. A crystal structure having an X-ray diffraction peak of Cukα rays at ˜56.5 ° and 56.5 ° to 59.5 °, and a bixbite crystal structure represented by In ₂ O ₃ , It is preferable to satisfy the composition ratio.

By including a bixbite crystal structure represented by In ₂ O ₃ , it is easy to manufacture a target having a low specific resistance without performing a reduction treatment.

  It is preferable that the oxygen content of the tissue having a large In content is lower than the oxygen content of other surrounding portions. The oxygen content of each tissue can be confirmed by a composition distribution using an electron probe microanalyzer (EPMA).

Further, the lattice constant a of the bixbyite structure represented by In ₂ O ₃ is preferably 10.14 or less, more preferably 10.10 or less, and particularly preferably 10.08 or less. The lattice constant a is obtained by XRD fitting. If the lattice constant is small, it can be expected that the specific resistance can be lowered by improving the mobility.

In the target of the present invention, substantially the same crystal type is 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 °. A crystal structure having X-ray diffraction peaks of Cukα rays at ˜56.5 ° and 56.5 ° to 59.5 °, and a homologous crystal structure represented by InGaO ₃ (ZnO), and It is preferable to satisfy the composition ratio.

By including both the new crystal type presumed to be the homologous crystal structure and the homologous crystal structure represented by InGaO ₃ (ZnO), when used as a target, there is little fluctuation in film formation speed, and the generation of white spots can be achieved. Effects such as few appearances, good bending strength, and less abnormal discharge can be expected.

Next, the manufacturing method of the sputtering target of the first present invention (hereinafter referred to as the first manufacturing method of the present invention) will be described.
The first production method of the present invention includes the following steps (a) to (e).
(A) A step of preparing a mixture by mixing raw material compound powders,
(B) forming the mixture to prepare a molded body having a thickness of 6.0 mm or more;
(C) a step of heating the atmosphere at a heating rate of 3 ° C./min or less,
(D) a step of further sintering the heated body at 1280 ° C. to 1520 ° C. for 2 hours to 96 hours to obtain a sintered body having a thickness of 5.5 mm or more,
(E) Grinding the surface of the sintered body by 0.25 mm or more

In the first production method of the present invention described above, among the targets of the present invention, substantially the same crystal type consists of only one type of crystal, and the one type of crystal type is represented by In ₂ Ga ₂ ZnO _7. A target having a homologous crystal structure and satisfying the composition ratio of the region 1, a target having a homologous crystal structure in which one type of crystal type is represented by InGaO ₃ (ZnO) and satisfying the composition ratio of the region 2, And a target that includes a spinel crystal structure represented by ZnGa ₂ O ₃ and a bixbite crystal structure represented by In ₂ O ₃ , wherein substantially the same crystal type satisfies the composition ratio of the region 1 or region 3, and The substantially identical crystal types are 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and 56. Of Cukα rays at 5 ° to 59.5 ° This is useful for manufacturing a target including a crystal structure having an X-ray diffraction peak and a bixbite crystal structure represented by In ₂ O ₃ and satisfying the composition ratio of the region 5.

  The average thickness of the molded body is usually 6.0 mm or more, preferably 8 mm or more. If it is 6.0 mm or more, in-plane temperature unevenness is reduced, and it can be expected that variations in the types of crystal types on the surface and in the deep part are less likely to occur.

The heating rate is usually 3.0 ° C./min or less, preferably 2.5 ° C./min or less, and particularly preferably 1.5 ° C./min or less. In addition, the lower limit of the temperature rising rate is about 0.3 ° C./min. If it is slower than 0.3 ° C./min, the sintering time may be excessively increased and the cost may increase.
If the rate of temperature rise is more than 3 ° C./min, the types of crystal types on the surface and in the deep part may fluctuate. This is presumably because temperature unevenness occurs in the thickness direction of the target when the temperature is raised.

The sintering temperature is usually from 1280 ° C to 1520 ° C, preferably from 1300 ° C to 1500 ° C.
The sintering time is usually 2 hours to 96 hours, preferably 4 hours to 48 hours, and more preferably 6 hours to 24 hours.

  The grinding depth is usually 0.25 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, and particularly preferably 2 mm or more. If it is less than 0.25 mm, there is a possibility that the fluctuation part of the crystal structure near the surface cannot be removed sufficiently.

The second production method of the present invention includes the following steps (a) to (e).
(A) A step of preparing a mixture by mixing raw material compound powders,
(B) forming the mixture to prepare a molded body having a thickness of 6.0 mm or more;
(C) a step of heating the atmosphere at a heating rate of 3 ° C./min or less,
(D) a step of further sintering the temperature-increased molded body at 1350 ° C. to 1540 ° C. for 2 hours to 36 hours to obtain a sintered body having a thickness of 5.5 mm or more;
(E) Grinding the surface of the sintered body by 0.25 mm or more

In the second production method of the present invention, among the targets of the present invention, substantially the same crystal type comprises one type of crystal type, and the one type of crystal type is represented by In ₂ Ga ₂ ZnO _7. This is useful for producing a target having a homologous crystal structure and satisfying the composition ratio of the region 1.

The sintering temperature is usually more than 1350 ° C. and not more than 1540 ° C., preferably 1380-1510 ° C., more preferably 1400-1490 ° C. When the sintering temperature is 1350 ° C. or lower or exceeds 1540 ° C., there is a possibility that a crystal type other than the above-described crystal type (homologous crystal structure represented by In ₂ Ga ₂ ZnO ₇ ) may be obtained.

Moreover, sintering time is 2 hours or more and 36 hours or less normally, 4 to 24 hours are preferable and 8 to 12 hours are more preferable. When the sintering time exceeds 36 hours, there is a possibility that a crystal type other than the above-described crystal type (homologous crystal structure represented by In ₂ Ga ₂ ZnO ₇ ) may be obtained.

  Other conditions are the same as those in the first production method of the present invention, and are omitted here.

The third production method of the present invention includes the following steps (f) to (i).
(F) mixing the raw material compound powder to prepare a mixture;
(G) forming the mixture to prepare a molded body;
(H) a step of heating the atmosphere at a heating rate of 10 ° C./min or less,
(I) A step of further sintering the temperature-increased compact at 1100 ° C. to 1350 ° C. for 4 hours to 96 hours.

In the third production method of the present invention, a spinel crystal structure represented by ZnGa ₂ O ₃ and a bixbite crystal structure represented by In ₂ O ₃ are substantially identical among the targets of the present invention. And a sputtering target satisfying the composition ratio of the region 1 or the region 3 is useful.

  The rate of temperature increase is usually 10 ° C./min or less, preferably 6 ° C./min or less, and more preferably 3 ° C./min or less. If the rate of temperature rise exceeds 10 ° C./min, properties such as the surface portion and the internal crystal form may change, or cracks may occur in the target. In addition, the lower limit of the temperature rising rate is about 0.3 ° C./min.

The sintering temperature is usually 1100 ° C. or higher and 1350 ° C. or lower, and preferably 1200 ° C. or higher and 1300 ° C. or lower. If it is less than 1100 ° C., the relative density may not be increased, and it may take time for sintering. When the temperature is higher than 1350 ° C., other crystal types generated at high temperature are generated, and the above crystal types (spinel crystal structure represented by ZnGa ₂ O ₃ and bixbite crystal structure represented by In ₂ O ₃ ) are obtained. There is a risk that it cannot be obtained stably.

  The sintering time is usually from 4 hours to 96 hours, preferably from 4 hours to 48 hours, and more preferably from 6 hours to 24 hours. If it is less than 4 hours, the relative density may not increase. If it is 96 hours or longer, part of the composition may evaporate and the composition ratio may vary, and it takes too much time for production and it is difficult to industrialize.

  Other conditions are the same as those in the first or second production method of the present invention, and are omitted here.

<Description of each target manufacturing process>
(1) Compounding step The compounding step is a step of mixing a metal oxide that is a raw material of the sputtering target.

  As the raw material, powders such as indium compound powder, gallium compound powder, and zinc compound powder are used. The specific surface area (BET specific surface area) of each metal compound as a target raw material can be measured by the method described in JIS Z 8830. Examples of the indium compound include indium oxide and indium hydroxide. Examples of the gallium compound include gallium oxide and gallium hydroxide. Examples of the zinc compound include zinc oxide and zinc hydroxide. As each compound, an oxide is preferable because it is easy to sinter and it is difficult to leave a by-product. Moreover, it is preferable to use metallic zinc (zinc powder) as a part of the raw material. When zinc powder is used as a part of the raw material, the generation of white spots can be reduced.

  The purity of the raw material is usually 2N (99% by mass) or more, preferably 3N (99.9% by mass) or more, particularly preferably 4N (99.99% by mass) or more. If the purity is lower than 2N, the durability of the resulting thin film may be reduced, or impurities may enter the liquid crystal side when used in a liquid crystal display, and baking may occur.

  It is preferable to mix the raw materials used for the production of the target such as metal oxide and uniformly mix and pulverize them using an ordinary mixing and pulverizing machine such as a wet ball mill, a bead mill or an ultrasonic device.

(2) Calcination process The calcination process is a process provided as necessary, after obtaining a mixture of compounds that are raw materials of the sputtering target, and then calcining the mixture.
When calcination is performed, it is easy to increase the density, which is preferable, but there is a risk of increasing the cost. Therefore, it is more preferable that the density can be increased without performing calcination.

In the calcination step, the metal oxide mixture is preferably heat-treated at 500 to 1200 ° C. for 1 to 100 hours. This is because the thermal decomposition of the indium compound, the zinc compound, and the tin compound may be insufficient under heat treatment conditions of less than 500 ° C. or less than 1 hour. On the other hand, when the heat treatment condition exceeds 1200 ° C. or exceeds 100 hours, coarsening of the particles may occur.
Therefore, it is particularly preferable to perform heat treatment (calcination) in the temperature range of 800 to 1200 ° C. for 2 to 50 hours.

  The calcined product obtained here is preferably pulverized before the following molding step and firing step.

(3) Molding step The molding step is a step of pressure-molding a mixture of metal oxides (or calcined product when the calcining step is provided) to form a compact. By this process, it is formed into a shape suitable as a target. When the calcination step is provided, the obtained calcined fine powder can be granulated and then molded into a desired shape by a molding process.

Examples of the molding process that can be used in this step include press molding (uniaxial press), mold molding, cast molding, injection molding, and the like. In order to obtain a sintered body (target) having a high sintering density. In this case, it is preferable to mold by cold isostatic pressure (CIP) or the like.
In addition, it is preferable to perform cold isostatic pressure (CIP), hot isostatic pressure (HIP), and the like after press molding (uniaxial pressing) to provide two or more molding processes in order to improve reproducibility.

When using CIP (cold hydrostatic pressure or hydrostatic pressure press), it is preferable to hold at a surface pressure of 800 to 4000 kgf / cm ² for 0.5 to 60 minutes. It is more preferable to hold at a surface pressure of 2000 to 3000 kgf / cm ² for ² to 30 minutes. Further, if the surface pressure is less than 800 kgf / cm ² , the density after sintering may not increase or the resistance may increase. If the surface pressure exceeds 4000 kgf / cm ² , the apparatus may become too large and uneconomical. If the holding time is less than 0.5 minutes, the density after sintering may not increase or the resistance may increase. If it exceeds 60 minutes, it may take too much time and be uneconomical.

  In the molding process, molding aids such as polyvinyl alcohol, methylcellulose, polywax, and oleic acid may be used.

(4) Sintering process A sintering process is a process of baking the molded object obtained at the said formation process.

  In this case, the sintering is preferably performed in an oxygen gas atmosphere or under an oxygen gas pressure. If sintering is performed in an atmosphere that does not contain oxygen gas, the density of the target obtained cannot be sufficiently improved, and the occurrence of abnormal discharge during sputtering may not be sufficiently suppressed.

  At the time of sintering, the temperature is increased at a temperature increase rate in the predetermined atmosphere. Alternatively, the temperature rise may be stopped once during the temperature rise and held at the holding temperature, and sintering may be performed in two or more stages.

  Moreover, the temperature lowering rate (cooling rate) of the atmosphere during firing is usually 4 ° C./min or less, preferably 2 ° C./min or less, more preferably 1 ° C./min or less, further preferably 0.8 ° C./min or less, Particularly preferred is 0.5 ° C./min or less. When it is 4 ° C./min or less, the desired crystal form of the present invention is easily obtained. In addition, cracks are unlikely to occur when the temperature drops.

(5) Reduction process A reduction process is a process provided as needed which performs a reduction process in order to reduce the bulk resistance of the sintered compact obtained at the said sintering process as the whole target.

Examples of the reduction method that can be applied in this step include a method using a reducing gas, vacuum firing, or reduction using an inert gas.
In the case of reduction treatment with a reducing gas, hydrogen, methane, carbon monoxide, a mixed gas of these gases and oxygen, or the like can be used.
In the case of reduction treatment by firing in an inert gas, nitrogen, argon, a mixed gas of these gases and oxygen, or the like can be used.

  In the present invention, reduction treatment (inert gas atmosphere such as argon or nitrogen, hydrogen atmosphere, or heat treatment in vacuum or low pressure) is preferably not performed. When the reduction treatment is performed, there is a risk that a difference in resistance value between the surface portion and the deep portion may be generated or amplified.

(6) Processing step The processing step is to cut the sintered body obtained by sintering as described above into a shape suitable for mounting on a sputtering apparatus, and to mount a jig such as a backing plate. It is the process provided as needed for attaching.

In order to use the oxide sintered body as a sputtering target material, it is preferable that the sintered body is ground with, for example, a surface grinder so that the surface roughness Ra is 5 μm or less. The target material has a surface roughness Ra of 0.5 μm or less, and preferably has a ground surface with no directivity. If Ra is larger than 0.5 μm or the polished surface has directivity, abnormal discharge may occur or particles may be generated.
Here, the sputtering surface of the sputtering target may be further mirror-finished so that the average surface roughness Ra may be 1000 angstroms or less. For this mirror finishing (polishing), a known polishing technique such as mechanical polishing, chemical polishing, and mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water) or lapping with loose abrasive lapping (abrasive: SiC paste, etc.), and then lapping by changing the abrasive to diamond paste Can be obtained by:

The surface is preferably finished with a diamond grindstone of No. 200 to 10,000, and particularly preferably finished with a diamond grindstone of No. 400 to 5,000. If a diamond grindstone smaller than No. 200 or larger than 10,000 is used, the target may be easily broken.
Such a polishing method is not particularly limited. The obtained sputtering target material is bonded to a backing plate.

  The thickness of the target material is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 6 mm. Further, a plurality of targets may be attached to one backing plate to make a substantially single target.

Next, air blow or running water washing can be used for the cleaning treatment. When removing foreign matter by air blow, it is possible to remove the foreign matter more effectively by suctioning with a dust collector from the opposite side of the nozzle. In addition, since the above air blow and running water cleaning have a limit, ultrasonic cleaning etc. can also be performed. This ultrasonic cleaning is effective by performing multiple oscillations at a frequency of 25 to 300 KHz. For example, it is preferable to perform ultrasonic cleaning by multiplying twelve types of frequencies at 25 KHz intervals between frequencies of 25 to 300 KHz.
In addition, the composition ratio (atomic ratio) of the produced target can be obtained by analysis using an induction plasma emission analyzer (ICP-AES).

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely using an Example, this invention is not limited at all by these Examples.

Example 1
(1) Production of target Two or more of the same oxide sintered bodies were produced simultaneously under the following conditions, and one was used for a destructive test (cut and evaluated).

(A) Raw material In ₂ O ₃ purity 4N, manufactured by Asian Physical Materials Co., Ltd. Ga ₂ O ₃ purity 4N, manufactured by Asian Physical Materials Co., Ltd. ZnO purity 4N, manufactured by High Purity Chemical Co., Ltd. (b) Mixing: Ball mill Mixed for 24 hours.
(C) Granulation: natural drying (d) molding:
Press molding, surface pressure 400 kgf / cm ² , 1 minute hold CIP (hydrostatic pressure press), surface pressure 2200 kgf / cm ² , 5 minute hold (e) Sintering: Electric furnace Temperature rising rate 1 ° C./min Sintering temperature 1300 ° C
Sintering time 20 hours Sintering atmosphere Oxygen atmosphere Cooling rate 0.3 ° C./min (f) Post-treatment: No heat treatment (reduction treatment) under reducing conditions was performed.
(G) Processing: A sintered body having a thickness of 6 mm was ground and polished to a thickness of 5 mm.
The upper and lower surfaces and sides were cut with a diamond cutter, and the surface was ground with a surface grinder to obtain a target material having a surface roughness Ra of 5 μm or less.
(H) One of the obtained sintered bodies for a target was cut at a site having a thickness of 2.5 mm for deep measurement.
(I) The surface of the obtained sintered body for target was blown with air and further subjected to ultrasonic cleaning for 3 minutes, and then bonded to a backing plate made of oxygen-free copper with indium solder to obtain a target. The surface roughness Ra of the target was 0.5 μm or less and had a ground surface with no directionality.

(2) Evaluation of target sintered body The obtained target sintered body was evaluated by the following method.

(A) Specific resistance Measured based on a four-probe method (JIS R 1637) using a resistivity meter (Mitsubishi Chemical Co., Ltd., Loresta), and the average value at 10 locations was defined as the resistivity value. The ratio (R1 / R2) was calculated from the specific resistance (R1) on the surface of the obtained sintered body for the target and the internal specific resistance (R2).

(B) X-ray diffraction measurement (XRD)
The target sintered body and its cut piece were directly measured under the following conditions to determine the crystal type.
・ Device: ULTIMA-III manufactured by Rigaku Corporation
-X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
・ 2θ-θ reflection method, continuous scan (1.0 ° / min)
・ Sampling interval: 0.02 °
・ Slit DS, SS: 2/3 °, RS: 0.6 mm

  The crystal form of the compound contained in the oxide sintered body was determined by collating with the JCPDS card shown in Table 3.

(C) Particle size (μm)
The particle diameter of the oxide crystal was measured with an electron probe microanalyzer (EPMA) and is shown in Table 1 as an average particle diameter.
(D) Composition ratio (atomic ratio)
A sample was taken from the target and analyzed with an induction plasma emission analyzer (ICP-AES) to determine the atomic ratio.

The identity of the crystal type is determined to be “identical” when there is no crystal type included in only one of the crystal types identified by XRD (all identified crystal types match), and included in only one of them. The case where there was a crystal form that was not determined was determined to be “not identical” (if the above was satisfied, a difference in peak intensity (about ± 50%) was also determined to be the same).
Moreover, the identity of the element composition ratio (atomic ratio) on the surface of the sintered body for the target and the inside was determined to be the same within ± 0.01 for each metal element.
It was judged that the same in both the target sintered body surface and the internal particle size were within 5 μm.
The identity of the specific resistance on the surface of the target sintered body and inside was judged to be the same within ± 50%.
The identity of the elemental composition ratio was judged by taking samples from the surface and the inside (the surface after cutting) and analyzing by ICP analysis to compare the composition ratio (atomic ratio).

(3) Production of TFT Using the completed sputtering target, the channel stopper type thin film transistor (reverse stagger type thin film transistor) of FIG. 1 was produced and evaluated.

  As the substrate 10, a glass substrate (Corning 1737) was used. First, 10 nm thick Mo, 80 nm thick Al, and 10 nm thick Mo were laminated in this order on the substrate 10 by electron beam evaporation. A gate electrode 20 was formed on the laminated film by using a photolithography method and a lift-off method.

A 200 nm thick SiO ₂ film was formed on the gate electrode 20 and the substrate 10 by the TEOS-CVD method to form the gate insulating layer 30. The gate insulating layer may be formed by sputtering, but is preferably formed by CVD such as TEOS (tetraethoxysilane) -CVD or plasma enhanced chemical vapor deposition (PECVD). In the sputtering method, off current may be increased.

  Subsequently, a semiconductor film 40 (channel layer) having a thickness of 50 nm was formed by RF sputtering using the target prepared in (1) above. Then, it heat-processed for 60 minutes at 300 degreeC in air | atmosphere.

A SiO ₂ film was deposited on the semiconductor film 40 as an etching stopper layer 60 (protective film) by sputtering. The protective film may be formed by a CVD method.

In this embodiment, the input RF power was 200 W. The atmosphere during the film formation was a total pressure of 0.4 Pa, and the gas flow rate ratio at that time was Ar: O ₂ = 95: 5. The substrate temperature was 50 ° C. The deposited oxide semiconductor film and protective film were processed into appropriate sizes by a photolithography method and an etching method.

  After the formation of the etching stopper layer 60, Mo having a thickness of 5 nm, Al having a thickness of 50 nm, and Mo having a thickness of 5 nm were laminated in this order, and the source electrode 50 and the drain electrode 52 were formed by photolithography and dry etching. .

  After that, heat treatment was performed at 300 ° C. for 60 minutes in the atmosphere to obtain a transistor having a channel length of 20 μm and a channel width of 20 μm.

(4) Evaluation of TFT Evaluation of the thin film transistor was performed as follows.
(A) Mobility (field effect mobility (μ))
Using a semiconductor parameter analyzer (Keutley 4200), the measurement was performed at room temperature in a light-shielded environment.

(B) S value (V / decade)
Using a semiconductor parameter analyzer (Keutley 4200), the measurement was performed at room temperature in a light-shielded environment.

(C) Mixed acid resistance
(i) Preparation of simple element for evaluating mixed acid resistance A simple element was prepared using a shadow mask. A shadow mask for forming a semiconductor layer was attached to a silicon substrate with a thermal oxide film (100 nm), and a semiconductor film was formed under the same conditions as in (3) above. Next, a shadow mask for forming a source / drain electrode is attached, and a gold electrode is formed by sputtering to form a source / drain electrode. A simple element for evaluating mixed acid resistance (TFT) having a channel length (L) of 200 μm and a channel width (W) of 1000 μm. ).

(ii) Evaluation of mixed acid resistance A simple element (TFT) for evaluating mixed acid resistance whose driving was confirmed was immersed in mixed acid (phosphoric acid aqueous solution, 30 ° C.) for 10 seconds, and then dried at 15 ° C. for 15 minutes with dry air. Later, TFT characteristics were measured. A gate current (Vg) of 15 V and a drain voltage (Vd) of 15 V were evaluated in two stages, with A indicating a drain current (Id) of 10 ⁻⁶ A or more and A indicating no drain current (Id).

(D) Evaluation of photocurrent Measurements under light irradiation and light-shielding environment were compared, and the threshold voltage (Vth) variation was evaluated in two stages, with A being less than 2V and A being 2V or more.

(5) Evaluation of stability during long-term use of sputtering target (a) Stability of film formation rate (variation)
The film formation rates before and after 1000 hours of continuous discharge (film formation) were compared.
A variation of less than 5% was evaluated as A, 5% or more but less than 10% was evaluated as B, and 10% or more was evaluated as C.

  The film formation rate (sputter rate) was determined by dividing the film thickness measured by a stylus type surface shape measuring device Decak (manufactured by ULVAC, Inc.) by the film formation time.

(B) Stability (variation) of TFT characteristics
A TFT was fabricated before and after 1000 hours of continuous discharge (film formation), and the variation in TFT characteristics (on-current) was evaluated. A sample having a variation of less than 10% was evaluated as A, a sample having a variation of 10% or more and less than 20% was evaluated as B, and a sample having a variation of 20% or more was evaluated as C.

(6) Others It was confirmed by measuring the composition distribution using an electron probe microanalyzer (EPMA) that the indium-rich portion of the surface and deep portions had a lower oxygen content than the surroundings.
Similarly, the difference in composition ratio with the target was evaluated using the thin film produced. The composition ratio was determined by analysis by ICP analysis. The composition ratio of the target and the thin film was almost the same (the composition ratio of each element of the thin film was within ± 2% of the composition ratio of each element of the target).

Examples 2-9 and Comparative Examples 1-8
An oxide sintered body, a sputtering target, and a TFT were prepared and evaluated in the same manner as in Example 1 except that the compositions and conditions shown in Table 2-1 and Table 2-2 were used. The results are shown in Table 2-1 and Table 2-2.
In addition, the Sn compound used in Example 3 and Reference Examples 1-3, 5 and 6 described later is as follows.
SnO ₂ purity 4N, manufactured by High Purity Chemical Co., Ltd. In Example 8, the lattice constant of the bixbite structure of In ₂ O ₃ obtained from XRD was lattice constant a = 10.074.

Examples 10 and 11
When the semiconductor film was formed with a thickness of 50 nm, it was normally on, so a TFT was manufactured with the semiconductor film as 15 nm. An oxide sintered body, a sputtering target, and a TFT were prepared and evaluated in the same manner as in Example 1 except that the thickness of the semiconductor film was 15 nm and the composition and conditions shown in Table 2-1 were used. The results are shown in Table 2-1.

In addition, by the measurement by EPMA, it has confirmed that the structure | tissue with much In content of Example 10 and 11 of the surface and the deep part had less oxygen content than the circumference | surroundings.
Moreover, the measurement by EPMA has confirmed that the structure | tissue with much In content of Example 3 in both the surface and the deep part has more tin (Sn) content than the circumference | surroundings.

Reference Examples 1-6
Table 2-3 shows reference examples of sintered bodies not containing Ga. It can be seen that the sintered body containing no Ga hardly changes in the crystal type in the thickness direction of the target. From this result, the long-term stability problem of the present invention is a prominent problem in the case of a sintered body containing Ga (in the case of a sputtering target containing indium oxide, gallium oxide and zinc oxide as raw materials). Can be confirmed.

Table 1 shows the elemental composition ratio (atomic ratio), particle size, and specific resistance of the target sintered bodies produced in Example 1 and Comparative Example 1.
Tables 2-1 to 2-3 show various characteristics and the like of target sintered bodies and TFTs prepared in Examples, Comparative Examples, and Reference Examples. “Δ” in the crystal form of the target means a trace component (impurity component, main peak height is 50% or less of main component main peak height).
Crystal type and JCPDS card No. Table 3 shows the comparison.

According to the present invention, it is possible to provide a sputtering target that is excellent in stability of characteristics of a thin film obtained when film formation is performed over a long period of time.
According to the present invention, a thin film transistor having stable TFT characteristics can be efficiently provided.

1 channel stopper type thin film transistor 10 substrate 20 gate electrode 30 gate insulating layer 40 semiconductor layer (channel layer)
50 Source electrode 52 Drain electrode 60 Etching stopper layer (protective film)

Claims (7)

Including In, Zn, and Ga,
A sputtering target composed of an oxide sintered body in which the crystal types of the surface and internal compounds are the same,
The In of the oxide sintered body, Zn, and the composition ratio of Ga is (atomic ratio), meets one of the following regions 4-6,
The same crystal type is 2θ = 7.0 ° to 8.4 °, 30.6 ° to 32.0 °, 33.8 ° to 35.8 °, 53.5 ° to 56.5 ° and 56. A sputtering target comprising a crystal structure having an X-ray diffraction peak of Cukα rays at .5 ° to 59.5 °.
Region 4
0.00 <Ga / (In + Ga + Zn) <0.15
0.20 ≦ In / (In + Zn) <0.51
0.58 <In / (In + Ga)
Region 5
0.00 <Ga / (In + Ga + Zn) ≦ 0.20
0.51 ≦ In / (In + Zn) ≦ 0.85
Region 6
0.15 ≦ Ga / (In + Ga + Zn)
In / (In + Zn) <0.51
0.58 <In / (In + Ga)   The ratio R1 / R2 between the specific resistance (R1) of the surface of the oxide sintered body and the specific resistance (R2) at a depth of t / 2 mm from the surface is 0.4 or more and 2.5 or less. The sputtering target described.   The sputtering target according to claim 1, wherein the same crystal type is composed of only one type of crystal type. The sputtering target according to claim 3, wherein the composition ratio of the region 4 is satisfied. The sputtering target according to claim 1, wherein the same crystal type further includes a bixbite crystal structure represented by In ₂ O ₃ and satisfies the composition ratio of the region 5. The sputtering target according to claim 1, wherein the same crystal type further includes a homologous crystal structure represented by InGaO ₃ (ZnO) and satisfies the composition ratio of the region 6. The manufacturing method of the sputtering target of Claim 3 including the process of following (a)-(e).
(A) A step of preparing a mixture by mixing raw material compound powders,
(B) forming the mixture to prepare a molded body having a thickness of 6.0 mm or more;
(C) a step of heating the atmosphere at a heating rate of 3 ° C./min or less,
(D) a step of further sintering the heated body at 1280 ° C. to 1520 ° C. for 2 hours to 96 hours to obtain a sintered body having a thickness of 5.5 mm or more,
(E) Grinding the surface of the sintered body by 0.25 mm or more